Hong Kong (which is in China for ones who don't know) doesn't have an army because China has its own army and has the responsibility to take care of Hong Kong. If Hong Kong has its own army, China would be outraged because its also like saying "We will use our Hong Kong army to rebel against you, China!"
Music can calm you down by casually humming a tune or listening to a song. Art can calm you down by expressing your feelings through a drawing but I personally find humming a weird, at-the-top-of-my-mind tune easier as it doesn't need other materials.
Cancer is a genetic type of thing and sadly it can last forever as it runs in the family. It can't be ended but can only be supported through advanced medical technology. On the other hand, starvation can be ended if you end poverty. So, ending all of cancer is more worth it compared to starvation.
To add to that, a quarter of the Earth's people live on barely US$2 a day, according to the World Bank. The money spent on space exploration can instead deal with problems we already face now, poverty. Even though scientists predict that Earth might be overpopulated in the future and not suitable for living, that is a problem in the future. Shouldn't we deal with problems we face at the present rather than look further on in the future?